Ken Adelman, President Reagan’s arms-control director, was at the fateful October 1986 weekend summit between Reagan and Soviet leader Mikhail Gorbachev. Not only was he an eyewitness to and participant in what proved to be an intensely dramatic event in the Cold War, he is also a very good writer. He captures the drama and tension of those 48 hours that transports the reader to the middle of each scene of Oct. 11-12 in Reykjavik, Iceland.

The Reykjavik meeting was the unforeseen summit. There had been staff-level exchanges between the two governments to have a preliminary meeting to plan for a full-scale summit in Washington late in 1987.

Then, on Sept. 15, Mr. Gorbachev replied to a July letter from Reagan that had restated U.S. arms proposals. In his six-page reply, the Soviet leader wrote defensively about his perception that the United States was carrying out a deliberate plan to delegitimize the USSR. Then, in the final page, he switched “from nasty to nice,” proposing “a quick one-on-one meeting, let us say in Iceland or London, maybe just for one day” with the subject to be arms control. He added that the two could “engage in a strictly confidential, private and frank discussion (possibly with only our foreign ministers present).”

Reagan who, for a long time, had been developing a strong desire to one day eliminate all nuclear weapons, saw such a meeting as an opportunity to talk about that possibility. Therefore, rushed planning began. Both men would go with small staffs.

Hofdi House was chosen as the site for the meetings. Owned by the Icelandic government, it stood by itself, simplifying security. About the size of a suburban American home (2,300 square feet) it would be just large enough for the principals to meet and for staff meetings on the second floor.

Mr. Adelman writes that what had been expected to be an uneventful weekend turned out to be “an emotional roller coaster, full of twists and turns, ups and downs all weekend long.”

At the Saturday morning meeting, Mr. Gorbachev took the initiative by announcing his agenda items. He proposed possible reductions of strategic weapons. On the second item, intermediate weapons, he said that British and French nuclear weapons could be left as is; however, American weapons should be removed from Europe. Recognizing the serious condition of the Soviet economy, he wanted strict adherence to the Anti-Ballistic Missile (ABM) Treaty and no Strategic Defense Initiative (SDI) by the Americans.

Reagan argued vigorously that “SDI makes the elimination of nuclear weapons possible.” His proposal was to field-test SDI with Soviet representatives observing. If the test proved practical, SDI technology would be shared with the USSR. Also, SDI would not be deployed until offensive strategic missiles were dismantled. Mr. Gorbachev was both skeptical and negative. Soviet intelligence had mistakenly concluded that SDI was much further along than it actually was. Mr. Gorbachev knew that the USSR could not bear a race over SDI, neither technologically nor economically.

He hinted that the United States could use space-based missiles to target the USSR, and he treated the shared technology offer as not serious.

The two agreed to continue their discussions in the afternoon. Along with Secretary of State George P. Shultz and USSR Foreign Minister Eduard Shevardnadze, they left for their respective embassies.

In the afternoon, Reagan sought to overcome Mr. Gorbachev’s skepticism about SDI.

There was thrust and parry, but no agreement except to turn the agenda items over to teams of American and Russian experts. Paul Nitze, a skilled U.S. negotiator, and Sergey Akhromeyev, decorated war hero and chief of the USSR general staff, led the two teams.

After a 3 a.m. break, Akhromeyev announced a breakthrough: The Soviets would agree to a 50 percent cut in strategic weapon down to equality. Mr. Adelman concludes in his book that “Akhromeyev served nobly at Reykjavik.” The session concluded at daybreak.

The Sunday morning session devolved quickly into previous positions argued by Reagan and Mr. Gorbachev. Before long, however, Reagan began to speak of the benefits of the “Zero Option” — the elimination of all nuclear weapons. Mr. Gorbachev agreed in principal.

At that point, Mr. Gorbachev said he could accept Reagan’s position on intermediate-range weapons. That is, treat the respective distribution both equally and in Asia as well as Europe. Reagan then agreed to Mr. Gorbachev’s proposal to uphold the ABM Treaty for another 10 years; however, when Mr. Gorbachev reiterated his proposal to restrict SDI to the laboratory, Reagan refused.

In the final session, Sunday afternoon, they argued over the wording of final statements drafted by Mr. Shultz and Mr. Shevardnadze. Both agreed to stating the goal of eliminating all nuclear weapons; however, Mr. Gorbachev made one last argument for keeping SDI in the laboratory, and Reagan once again said he could not agree. Thus, the meeting ended with no agreement and no joint statement.

News media and many others concluded that Reykjavik had been a failure. Time and history, however, have proved that it was the climactic event of the Cold War. Mr. Gorbachev had to go home and hasten the reforms he had begun. This turned out to be an irreversible process. As it was, Reagan’s stand proved to be the last word.

Peter Hannaford is a board member of the Committee on the Present Danger. His latest book is “Presidential Retreats” (Threshold Editions, 2012).